Since an outbreak began last October, there have been 470 cases reported in Ontario by 11 different public health units.
Ottawa Public Health is preparing for measles in the city as cases continue to surge across Ontario.
There have been no cases in Ottawa during what is now the largest measles outbreak the province has seen since it was eliminated in 1998 due to high vaccination rates.
But in a memo to the mayor, city council and the Ottawa Board of Health this week, interim medical officer of health Dr. Trevor Arnason said Ottawa Public Health was continuing to promote vaccination and to prepare for potential measles diagnoses.
Measles is one of the most contagious infectious diseases known to mankind, which makes public health efforts to contain it crucial. As many as 90 per cent of susceptible people exposed to the virus will become infected, and the virus can remain in the air and on surfaces for several hours after an infected person has left an area.
On Thursday, Public Health Ontario revealed there had been 120 new confirmed and probable measles cases across the province in a rapid spike during the past week alone. That brought the total number of cases in 2025 to 440, the vast majority among people who had been unvaccinated. Since the outbreak began last October, there have been 470 cases reported in Ontario by 11 different public health units.
Most of the cases reported have been in southwestern Ontario. The South East Health Unit, which replaced smaller health units in Kingston, Prince Edward County and surrounding areas as well as the Leeds, Grenville and Lanark District Health Unit, has reported 35 cases.
Arnason noted that vaccination was the most effective way to prevent measles.
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Vaccination rates, which were once above 95 per cent in Ontario, have slipped in recent years, in part because of the COVID-19 pandemic, but also because of hesitancy and misinformation as well of lack of access to primary care.
Among other initiatives to improve vaccination rates is the Kids Come First health team and others who have been offering routine childhood immunization appointments for those who do not have timely access to primary care. More information is available online at parentinginottawa.ca/en/immunizations.aspx.
Ottawa Public Health Neighbourhood Health and Wellness Hubs and community vaccination clinics have administered more than 23,000 routine immunizations to children and youth who may have difficulty accessing health-care providers, Arnason said.
OPH is also sending notices to students with incomplete vaccination records.
Although it is difficult to get real-time data on vaccination rates in Ontario, some have speculated that public health’s ongoing focus on making it easier for children to catch up on routine immunization in Ottawa could be one reason there have, so far, not been any measles cases in the city. But, given the rapid spread across the province, the risk of measles cases in the city is high.
Suspected and lab-confirmed cases in the city must be reported to OPH by physicians, nurse practitioners, labs and hospitals, Arnason said. He added that public health had proactively shared information about measles with local health-care providers.
If it receives a report of a measles diagnosis OPH is required to follow up with people who are diagnosed and their potential contacts. It will notify residents at risk by direct communication or by public service announcements.
“OPH is at the ready to support individuals diagnosed with measles, conduct contact tracing at locations where possible measles exposures have occurred and provide outreach to healthcare professionals,” he said.
Arnason noted that more serious cases of measles can lead to pneumonia and can have “wide-ranging and sometimes lifelong consequences, including blindness, deafness and brain damage.”
Since Ontario’s outbreak began in October, 34 people, mostly children, have required hospitalization, including two in intensive care. Thirty-two of those cases were in people who had been unimmunized, including 29 children.
Children receive their first routine measles vaccines around age one and second ones later. Infants at high risk can receive doses of measles vaccine as early as six months.
During the decade between 2013 and 2023, there were 101 confirmed cases of measles reported in Ontario — less than one-quarter of the cases reported in the first three months of 2025.
Symptoms of measles include fever, red blotchy rashes, red watery eyes and coughing.
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